Optical scanning device

The present invention relates to an optical scanning device having a MEMS optical deflector.

Patent Literature 1 discloses an optical scanning device having a MEMS optical deflector. The optical scanning device is attached to a temple (side support) on one side of a spectacles-type head mount, emits scanning light from the MEMS optical deflector toward lenses and half mirrors arranged toward the front (front frame) of the spectacles, and projects an image on the user's retina by the scanning light reflected by the half mirror.

According to the schematic diagram of Patent Literature 1, the lens and the half mirror are mounted on the temple in addition to the optical scanning device, and the optical scanning device faces the half mirror with the lens interposed therebetween. Laser light emitted from the optical scanning device scans on the half mirror along the mirror surface thereof, is reflected by the mirror surface, and projects an image onto the retina of a user's eye.

Patent Literature 1 does not disclose in what positional relationship, the light source, the MEMS optical deflector, and the substrate are mounted in the optical scanning device specifically.

An object of the present invention is to provide an optical scanning device which has improved the quality of a light beam emitted as scanning light.

An optical scanning device of the present invention includes:

According to the present invention, a shielding plate arranged for a corresponding optical path generation mirror has an aperture. Thus, a light beam can be improved into a light beam with high contrast as a result of cutting a peripheral low brightness area by the aperture.

A plurality of preferred embodiments of the present invention will be described in detail with reference to the drawings. It goes without saying that the present invention is not limited to the following embodiments. In addition to the following embodiments, the present invention includes various configuration modes within the scope of the technical idea of the present invention. The same elements are given the same reference numerals through all the drawings.

(Overall Configuration)

is a plan view of an optical scanning device,is a view taken along arrowB in,is a view taken along arrowC in, andis a view taken along arrowD in. Incidentally,show the optical scanning devicewith a cover(one-dot chain line in) removed.

The optical scanning deviceincludes a support frame body. The support frame bodyhas an L-shaped cross-sectional contour, and has a bottom plate portionand an uprising plate portionwhich are vertically connected. A substrateis rectangular and placed onto and fixed to an upper surface of the bottom plate portion

For convenience of description, a three-axis orthogonal coordinate system is defined. An X-axis and a Y-axis are defined as axes in the directions parallel to the longitudinal direction (direction parallel to the long side) and the lateral direction (direction parallel to the short side) of the substrate, respectively. A Z-axis is defined as an axis parallel to the uprising direction of the uprising plate portionfrom the substrate.

Lp indicates a light beam. The course of the light beam Lp means an optical path of the light beam Lp. C1 is an optical axis as a central axis of the optical path of the light beam Lp. The optical path is static between a VCSELand a MEM optical deflector. Since the light beam Lp is emitted from the MEM optical deflectoras scanning light, an optical path on the downstream side from the MEMS optical deflectorbecomes dynamic.

In the optical scanning device, the light beam Lp is emitted from the left side of, i.e., from the negative end of the optical scanning devicein the X-axis direction. Therefore, in the X-axis, the negative side and the positive side will be appropriately referred to as the front and rear of the optical scanning device, respectively. Further, since the positive side and the negative side in the Z-axis direction are respectively taken as an upper surface and a lower surface in the substrate, the positive side and the negative side in the Z-axis direction will be appropriately defined as above and below the optical scanning device.

The VCSELand the MEMS optical deflectorare mounted on the upper surface of the substratewith the X-axis direction as an arrangement direction. The VCSELhas an emission uniton its upper surface and emits laser light upward, i.e., just above in parallel to the Z-axis direction from the emission unit. The MEMS optical deflectordirects a mirror surface of a rotating mirrorupward.

Incidentally, although the MEMS optical deflectoris a two-dimensional scanning MEMS optical deflector in the present embodiment, it may be a one-dimensional scanning MEMS optical deflector. The configuration of the MEMS optical deflector itself is known in various ways. For example, the MEMS optical deflectors described in Japanese Patent Application Laid-Open No. 2017-207630 (two-dimensional scanning MEMS optical deflector) and Japanese Patent Application Laid-Open No. 2014-056020 (one-dimensional scanning MEMS optical deflector) are selected.

A lens() is arranged directly above the emission unitin proximity to the emission unit. In, the VCSELis illustrated as a single body, but in an actual product, it is enclosed in a package (not shown). The package which encloses the VCSELtherein is made of a transparent material such as quartz glass at a portion through which the light beam from the emission unitis emitted (for example: Japanese Patent No. 4512330 and Japanese Patent Application Laid-Open No. 2009-027088). The lensis fixed (for example, glued) to an inner or outer surface of such a transparent material, or a transparent part itself thereof is processed as a lens, so that the position directly above the emission unitis held.

is a side view of the support frame body. Description will be made about the support frame body, a plate-like mirror, and a rotary type mirrorwith reference toand.

The uprising plate portionof the support frame bodyhas an inclined grooveand a through hole. The inclined groovehas a rectangular cross section and opens obliquely rearward upward along the side contour of the uprising plate portion. A bottom surface of the inclined grooveis formed of an inclination surface inclined at 45° with respect to the substrate. The through holeis formed as a cylindrical hole penetrating through the uprising plate portionin the Y-axis direction.

In the X-axis direction, the center of the width (length in side view in) of the inclination surface (bottom surface) of the inclined grooveis located at the same position as the emission unitof the VCSEL. In the X-axis direction, a center line Co of the cylindrical hole of the through holeis positioned between the VCSELand the rotating mirrorof the MEMS optical deflectorin the X-axis direction. The center of the length of the inclination surface of the inclined grooveand the center line of the cylindrical hole of the through holeare located at the same position in the Z-axis direction, that is, at the same height from the substrate.

The plate-like mirroris made of a rectangular plate-like member and has one end adhered to a slope portion of the inclined groovein a cantilevered state with an adhesive member such as a resin with the lower plate surface thereof used as a mirror surface. The plate thickness of the plate-like mirroris set substantially equal to the depth of the inclined groove.

The plate width (length in side view in) of the plate-like mirroris slightly shorter than the width (length in side view in) of the inclined groove. Therefore, before one end of the plate-like mirroris adhered to the inclined groove, that is, in a state before the one end is fixed, the plate-like mirroris slightly displaceable in the direction of the slope of the bottom surface within the inclined grooveand is capable of changing the angle of rotation around the axial line parallel to the Y-axis. Such a change enables adjustment of the orientation of the mirror surface of the plate-like mirrorwhen manufacturing the optical scanning device. By adhesion of one end of the plate-like mirrorto the inclined groove, the plate-like mirror is fixed so that it cannot be displaced.

The rotary type mirrorhas a flat plate-like mirror portionand a cylindrical fitting end portionwhich is coupled to one end of the mirror portionand fits into the through hole. The diameter of the fitting end portionis slightly smaller than the diameter of the through hole. Therefore, before adhesion of the fitting end portionto the through hole, i.e., in a state before fixing thereof, the rotary type mirroris rotatable about the center line of the through holewhile fitting the fitting end portioninto the through hole, and can be tilted within a predetermined inclination angle range from a state in which the center line of the rotary type mirroris aligned with the center line Co () of the through hole. Therefore, the rotary type mirroris rotatably displaceable in a larger angle range than the plate-like mirror. Such a rotatable and tiltable configuration enables adjustment of the orientation of the mirror surface as the lower surface of the mirror portionwhen manufacturing the optical scanning device, and then allows the fitting end portionto be fixed so as not to rotate by adhering it with an adhesive member such as a resin.

The rotating mirrorof the MEMS optical deflectoris not positioned directly below the rotary type mirrorwith respect to the rotary type mirrorbut is positioned on the front side, i.e., on the negative side with respect to the rotary type mirrorin the X-axis direction. In other words, the rotating mirrorof the MEMS optical deflectoris positioned obliquely downward when viewed from the rotary type mirror.

As will be described later, this configuration contributes to causing the light beam Lp from the optical scanning deviceto be emitted obliquely forward rather than perpendicular to the substratein regard to its emission direction. This configuration ensures that when the optical scanning deviceis attached to the temple of a spectacle body as a spectacles-type video display device(video scanning device of smart glass) described as a use example of the optical scanning device in the next, the light emitted from the optical scanning devicereaches the lens inner surface of the spectacle body without being interfered by the user's face from a slight gap between an imaging device and the user's face.

is a view showing the spectacles-type video display deviceas an application example of the optical scanning device. The spectacles-type video display devicewill be briefly described. The spectacles-type video display deviceincludes a spectacle bodyand a video generation devicedetachably attached to the spectacle bodyby a mounting member such as a clip. The spectacle bodyincludes left and right templesandand a front framecoupled to front ends of the left and right templesandat both left and right ends. The front framefurther includes left and right lens frame portionsand, and a bridgeconnecting the left and right lens frame portionsand

The optical scanning deviceis incorporated in one-row arrangement within the video generation devicetogether with other elements (for example: buffer amplifier for MEMS sensor and LDD (laser driver)) along the extension direction of the templeof the spectacle body. Incidentally, in this one-row arrangement, the optical scanning deviceis arranged in the forefront, that is, closest to the lensside. Thus, the light beam Lp (or) emitted from the optical scanning devicescans a scanning regionas a region on the inner surface side of the lens. The scanning regionis a half mirror, and the light beam Lp is reflected by the scanning regionto generate an image on the user's retina with the retina as a screen.

The cover() extends along the contour of the uprising plate portionabove the substrate, and is placed over the uprising plate portionto fix an opening peripheral edge on the lower end side thereof to the peripheral edge of the bottom plate portion. The coverhas a transparent portionat least at a portion where a light beam Lp to be described later is emitted from the optical scanning deviceas scanning light.

(Configuration of Main Part)

is a detailed view of a positional relationship of optical elements of the optical scanning devicein which the optical path of the light beam Lp is arranged,is a view taken along arrowB in,is a view taken along arrowC in,is a view taken along arrowD in, andis a view taken along arrowE in.is also a view taken along arrowC′ in. Incidentally, the arrowsB toE andC′ inare all located on the optical axis C1.

Incidentally, in, the right side on the drawing is forward in the negative direction of the X-axis, and the left side thereon is backward in the positive direction of the X-axis.

The lensand the plate-like mirrorare arranged directly above the emission unit. The plate-like mirrorhas a mirror surface which faces obliquely downward toward the rotary type mirror. A shielding platehas an elliptical apertureand is fixed (e.g., glued) to the mirror surface of the plate-like mirror. Consequently, the mirror surface of the plate-like mirrorallows the light beam Lp to enter and exist only within the range of the elliptical aperture.

The lensis positioned between the emission unitand the plate-like mirrorin the optical path of the light beam Lp and emits the light beam Lp emitted from the emission unitwhile expanding in the radial direction so as to converge on a predetermined point (in this example, a light spoton a projection screen) downstream of the MEMS optical deflector. Thus, after the light beam Lp exits through the lens, it advances to the predetermined point while shrinking in a light radial direction.

In the rotary type mirror, the mirror surface of the mirror portionfaces obliquely downward toward the plate-like mirrorside. The optical axis C1 extends parallel to the substratebetween the plate-like mirrorand the mirror portion. A shielding platehas an elliptical apertureand is fixed (e.g., glued) to the mirror surface of the mirror portion. Thus, the light beam Lp is incident only within the range of the elliptical apertureon the mirror surface of the mirror portionof the rotary type mirror. The plate-like mirrorhas a lower surface as the mirror surface. The shielding platehas the elliptical apertureand is fixed to the mirror surface of the plate-like mirror. Thus, the mirror surface of the plate-like mirrorallows the light beam Lp to enter and exit only within the range of the elliptical aperture.

The light spotis generated on the projection screenas a condensing point of the light beam Lp by the lens. The projection screenwill be a location a predetermined distance away from the optical scanning devicealong the optical path of the light beam Lp. In the optical scanning deviceinstalled in the spectacles-type video display device(), the projection screenbecomes the user's retina. Incidentally, the light beam Lp emitted from the emission unitof the VCSELis laser light weakened enough to not harm human eyes.

(Operation)

The light beam Lp is emitted from the emission unitof the VCSELwhile spreading radially upward (positive direction in the Z-axis direction) perpendicular to the substrate. After passing through the lens, the light beam Lp advances along the optical path while reducing in the radial direction until it reaches the condensing point (light spotin the optical scanning device) of the lens. After passing through the lens, the light beam Lp passes through the elliptical apertureof the shielding plateand reaches the plate-like mirror.

In, the elliptical apertureis an ellipse as shown inwhen viewed from the direction perpendicular to the shielding plate(the normal direction of the plate-like mirror). The shielding platehas a surface inclined with respect to the optical axis C1. The major axis of the elliptical apertureoverlaps the optical axis C1 of the light beam Lp when viewed from the direction (normal direction) perpendicular to the shielding plate. In, Da1 and Db1 are the dimensions of the major axis and minor axis of the ellipse. Further, Da1/Db1 is defined as β1.

In, when the direction of the optical axis C1 is viewed from the upstream side (lensside) and the downstream side (rotary type mirrorside), the elliptical apertureis closer to a perfect circle than when viewed from the direction (normal direction) perpendicular to the shielding plate. That is, when the elliptical apertureis viewed from the direction of the optical axis C1, it is a circular shape in which the ratio of the major axis to the minor axis of the ellipse in(in, the elliptical apertureis an ellipse including a perfect circle) is closer to 1 than β1 (1<β1). In, the vertical axis becomes the major axis and the horizontal axis becomes the minor axis. Here, the diameter of the circle (the average value of the major and minor axes in the case of the ellipse) when viewed along the optical axis C1 is defined as α1.

The light beam Lp which is emitted from the emission unitof the VCSEL, passes through the lensand is condensed becomes a shape close to a perfect circle at any position on the optical axis C1 when viewed in the direction of the optical axis C1 (). The light beam Lp generates an elliptical irradiation shape Lp1 at the shielding platearranged obliquely with respect to the optical axis C1 (). The elliptical aperturebecomes an ellipse which is substantially similar in shape to the irradiation shape Lp1 but slightly smaller than it. Also, the elliptical apertureis included inside the irradiation shape Lp1. By doing so, the light beam Lp holds the shape close to the original perfect circle when viewed from the direction of the optical axis C1 even after being reflected by the plate-like mirrorand passing through the elliptical aperture.

However, the act of making the elliptical apertureinto the shape substantially similar to the irradiation shape Lp1 is limited to the case where the shielding plateis thin in thickness. When the thickness is taken into consideration, the shape is slightly deformed from the similar shape. Further, since the plate-like mirroris adjusted in inclination angle as described above, the inclination angle of the fixed shielding platechanges, and the accurate shape of the irradiation shape Lp1 is determined after the adjustment. For this reason, the relationship between the shapes of the elliptical apertureand the irradiation shape Lp1 may deviate from similarity, but the direction of the major axis always becomes the direction of inclination of the shielding platewith respect to the optical axis C1. Further, the ellipse of the elliptical apertureand the ellipse of the irradiation shape Lp1 have the intersection of the major and minor axes as the central position at the same location ().

Here, in order to consider an illuminance distribution in the cross section of the light beam Lp, a predetermined value γ1 is defined for the illuminance γ in the cross section. Incidentally, the illuminance γ in the cross section of the light beam Lp is maximum in the center of the cross section, i.e., at the point of intersection with the optical axis C1, and decreases as it moves away from the optical axis C1 in the radial direction, finally resulting in 0. The irradiation shape Lp1 is defined as a region in which the illuminance γ is equal to or greater than a predetermined value γ2 (0<γ2<γ1). The predetermined values γ1 and γ2 are 0.5 and 0.3 times the maximum value of the illuminance γ, respectively.

Incidentally, for convenience of description, it is assumed that a light ray passing through each position on the cross section reaches the projection screenwhile maintaining the illuminance at the position (where a loss actually exists). Further, the illuminance of the light spoton the projection screenis assumed to be the illuminance generated by converging the incident points of the respective light rays on the projection screento the light spot.

By passing through the elliptical aperture, the light beam Lp is cut in the peripheral edge in the cross section, in other words, in a radially outer region in which the illuminance γ is less than γ1. The region inside the irradiation shape Lp1 and outside the elliptical apertureinis the region to be cut. As a result, the light beam Lp immediately after being reflected by the plate-like mirrorand emitted from the elliptical aperturebecomes a light beam which is γ1 or more in the illuminance γ and circular in cross section. The light beam Lp then travels along the optical path toward the rotary type mirror.

The light beam Lp passes through the elliptical apertureof the shielding plateand reaches the rotary type mirror. As with the elliptical apertureof the shielding plate, the elliptical apertureis an ellipse when viewed in the direction of the optical axis C1 from the direction (the normal direction of the rotary type mirror) perpendicular to the shielding plate(). An irradiation shape Lp2 of the irradiation region of the light beam Lp within the elliptical apertureis an ellipse and is generated inside the ellipse of the elliptical aperture.

A dimension ratio β between the major and minor axes of the elliptical apertureis assumed to be β2 (=Da2/Db2). There is a relationship of β1≠β2.

When the optical axis direction is viewed from the upstream side (plate-like mirrorside) and the downstream side (MEMS optical deflectorside) (), the elliptical apertureis closer to a perfect circle than when viewed from the vertical direction, i.e., a circular shape in which the ratio between the major and minor axes is closer to 1 than β2. The diameter α of this circle is assumed to be α2. α1>α2 is made.

Since the elliptical aperturesandare different in the angle of inclination with respect to the optical axis C1, the shapes of the ellipses are not similar. Thus, even though the elliptical aperturesandare both circular when viewed from the direction of the optical axis C1, it is possible to set β1≠β2. It is preferable to make the major axis of the elliptical aperture longer as the shielding plate arranged to be inclined at an angle at which the inclination angle is large relative to the optical axis C1 of the light beam Lp (the direction perpendicular to the optical axis C1 is defined as an inclination angle=0°) is taken, that is, to increase the dimension ratio β.

The light beam Lp passes through the elliptical apertureand is then irradiated to the rotary type mirrorin an irradiation shape Lp2. The irradiation shape Lp2 is an elliptical shape smaller than the elliptical aperture.